The process of inflammation involves hemodynamic changes, increases in vascular permeability and the accumulation of leukocytes in various organs of the body. To simplify a very complex series of interactions we have devised two in vitro models of inflammation which enable us to eliminate serum and connective tissue components and determine the direct effects of various inflammatory mediators on the endothelium or epithelium itself or on the process of neutrophil and/or monocyte transendothelial/ transepithelial migration. The systems involve growing monolayers of either human umbilical vein endothelial cells on the connective tissue of amnion or kidney epithelial cells on micropore filters. These systems produce a transepithelial electrical resistance as high as 78 and 500 ohms.square cm, respectively. The effect of 1) leukocyte (neutrophil and mononuclear phagocyte), 2) chemoattractant (C5a and leukotriene B4), and/or 3) permeability factors (leukotriene C4&D4,C3a, platelet-activating factor, and prostaglandin E2) on the disassembly, reassembly and permeability of the endothelial and epithelial occluding junctions will be determined. This will be examined by continuous transepithelial electrical resistance studies, ultrastructural or radioactive tracer studies and freeze-fracture electron microscopy. The role of protein synthesis on the reassembly of the occluding junction will be studied. The effect of various chemo-attractants and permeability factors on arachidonic acid metabolism in human umbilical vein endothelial cells in situ as well as those grown in culture will be determined. Release of radiolabel from endothelial cells prelabeled with 3H-arachidonic acid will provide a quantitative measure of the release of arachidonic acid-derived products and a means to determine by reverse-phase HPLC the arachidonic acid metabolites synthesized in response to various stimuli. In addition, differences in the rate, ability to invade as well as possible interactions between monocytes and neutrophils during the transendothelial/epithelialmigratory process will be determined. The changes and interactions of these phagocytes as they remain in the connective tissue and the subsequent ability to leave the connective tissue will be examined. The results of these studies should provide insight into the inflammatory response and should increase our abilities to foster its beneficial effects and to limit its destructive sequelae.